1. Field of the Invention
This invention relates to a mechanical cam type zoom lens device.
2. Description of the Related Art
A zoom lens is provided with a zooming mechanism. In the zoom lens, a subject distance is kept unchanged during a zooming operation and even after the zooming operation. A general mechanical cam type zoom lens includes two or more lens groups coupled to a cam cylinder. When the zoom lens is to be zoomed, a cam ring is turned so that each lens group is moved along a cam groove of the cam cylinder. A focusing ring is turned so that one or more lens groups coupled to a body tube by screws or the like are moved. Thus, zooming and focusing are carried out by different lens groups in the zoom lens, and focusing is not carried out during zooming when a stationary subject is photographed.
The aforementioned mechanical cam type zoom lens device is composed of a number of components. When components of the lens and a zooming mechanism and the like have errors, a locus of a cam groove proper to the lens is changed such that the lens becomes out of focus during zooming. In view of this problem, the dimensional accuracy of the components has generally been improved. However, improving the dimensional accuracy of the components increases the production cost and reduces the yield in a step of manufacturing the components.